Low glyphosate doses change reproduction and produce tolerant offspring in dense populations of Hordeum vulgare

An investigation of spray drift deposition of glyphosate from an herbicide spraying train and its potential impact on non-target vegetation and railway ditches

Spray drift of glyphosate has the potential to affect non-target vegetation and surface waters close to the application area. To assess the likelihood of such impact along Swedish railways, four field experiments were conducted at three railway sites during 2019 and 2020. An herbicide spraying train applied herbicide Roundup Ultra (glyphosate) at speeds of 33 to 48 km/h. Quantitative filter papers were placed at 0.5, 1, 1.5, 2, 3 and 5 m distances to capture spray droplets. Wind speeds were low (0-2 m/s), but were found to be representative of normal operating conditions. Spray deposition decreased rapidly with distance, declining from 1800 g a.e./ha to an average of 5 g/ha within 1 m. Predicted 90th percentile drift rates suggested potential impact on vegetation within distances <1 m, where 90th percentile spray deposition would range from full dose to 18 g/ha. Beyond 1.5 m from the sprayed area, impact on vegetation was deemed unlikely. The potential concentrations in ditches near railways did not exceed the 100 μg glyphosate/L environmental quality standard even for ditches situated only 0.5 m from the sprayed area, indicating low risk to ditches or final recipients. Actual impact on vegetation was assessed using weed coverage data recorded by the herbicide spraying train itself. We extracted average weed coverages for 10 m sections around the edges of no spray zones and focused on the outermost sections surveyed, 0.35 to 1.4 m outside the application area. Predicted 90th percentile glyphosate deposition ranged from 565 to 6 g/ha, averaging 80 g/ha in this zone. By comparing no spray zones to adjacent track sections, and tracks treated with glyphosate in 2019 to those that were not, we demonstrate that there is a statistically significant but relatively minor effect of spray drift on non-target vegetation close to the track.

Intergenerational consequences of an auxin-like herbicide on plant sensitivity to a graminicide mediated by a fungal endophyte

In agroecosystems, herbicides are the predominant anthropogenic selection pressure for agriculture weed species. While weeds are the primary target, herbicides can have adverse impacts on non-target plant beneficial microorganisms. We aimed to investigate the influence of a foliar endophytic fungus (Epichloë occultans) on the sensitivity of Lolium multiflorum to a graminicide herbicide (diclofop-methyl) during both plant ontogeny and progeny. Susceptible individuals to diclofop-methyl with and without endophyte were pre-exposed to the auxin 2,4-D herbicide. This herbicide is known to stimulate the metabolic detoxification mechanism (CYP-450) of diclofop-methyl. Regardless of the endophyte, 2,4-D pre-treatment increased mother plant survival to nearly 100 % under diclofop treatment but not in the progeny. Furthermore, maternal plant exposure to 2,4-D reduced endophyte transmission to the seeds and from seed-to-seedlings. Our findings suggest that, despite a reduction in diclofop-methyl sensitivity during the ontogeny of mother plants, 2,4-D-mediated induction of likely CYP-450 metabolism is not intergenerationally transmitted and shows detrimental effects on the symbiotic endophyte persistence.

Environmental hormesis in living systems: The role of hormetic trade-offs

Hormesis (low-dose stimulation and high-dose inhibition) can be accompanied by hormetic trade-offs, that is, stimulation of some traits and inhibition (trade-off 1) or invariability (trade-off 2) of others. Currently, trade-off options and their biological significance are insufficiently studied. Therefore, the review analyses trade-off types, their relationship with asynchronous stress responses of indicators, the importance of trade-offs for preconditioning, hormesis transgenerational effects, fitness, and evolution. The analysis has shown that hormetic trade-offs 1 and 2 can be observed in evolutionarily distant groups of organisms and at different biological levels (cells, individuals, populations, and communities) with abiotic and biotic stressors, as well as various pollutants. Trade-offs 1 and 2 are found both between different functional traits (e.g., self-maintenance and reproduction in animals, growth and defense in plants), and between the endpoints of the same functional trait (e.g., seed weight and seed number in plants). Asynchronous responses of indicators to a low-dose stressor can lead to hormetic trade-offs in two cases: 1) these indicators have different responses (hormesis, inhibition or zero reaction) in the same dose range; 2) these indicators have hormetic responses with different hormetic zones. Trade-offs can have a positive, negative or zero effect on preconditioning, offspring, and fitness of the population. Trade-offs can potentially affect evolution in two ways: 1) the creation of trends in genotype selection; 2) participation in the assimilation of phenotypic adaptations in the genotype through the Baldwin effect (selection of mutations copying adaptive phenotypes).

Plant hormesis: Revising of the concepts of biostimulation, elicitation and their application in a sustainable agricultural production

Current research in basic and applied knowledge of plant science has aimed to unravel the role of the interaction between environmental factors and the genome in the physiology of plants to confer the ability to overcome challenges in a climate change scenario. Evidence shows that factors causing environmental stress (stressors), whether of biological, chemical, or physical origin, induce eustressing or distressing effects in plants depending on the dose. The latter suggests the induction of the "hormesis" phenomenon. Sustainable crop production requires a better understanding of hormesis, its basic concepts, and the input variables to make its management feasible. This implies that acknowledging hormesis in plant research could allow specifying beneficial effects to effectively manage environmental stressors according to cultivation goals. Several factors have been useful in this regard, which at low doses show beneficial eustressing effects (biostimulant/elicitor), while at higher doses, they show distressing toxic effects. These insights highlight biostimulants/elicitors as tools to be included in integrated crop management strategies for reaching sustainability in plant science and agricultural studies. In addition, compelling evidence on the inheritance of elicited traits in plants unfolds the possibility of implementing stressors as a tool in plant breeding.

Changes in the herbicide sensitivity and competitive ability of Abutilon theophrasti over 28 years: Implications for hormesis and weed evolution

BACKGROUND

The potential of weed species to respond to selection forces affecting the evolution of weedy traits such as competitive ability is poorly understood. This research characterized evolutionary growth changes in a single Abutilon theophrasti Medik. population comparing multiple generations collected from 1988 to 2016. A competition study was performed to understand changes in competitive ability, and a herbicide dose-response study was carried out to assess changes in sensitivity to acetolactate synthase-inhibiting herbicides and glyphosate over time.

RESULTS

When grown in monoculture, A. theophrasti biomass production per plant increased steadily across year-lines while leaf number decreased. In replacement experiments, A. theophrasti plants from newer year-lines were more competitive and produced more biomass and leaf area than the oldest year-line. No clear differences in sensitivity to imazamox were observed among year-lines. However, starting in 1995, this A. theophrasti population exhibited a progressive increase in growth in response to a sublethal dose of glyphosate (52 g a.e. ha-1 ), with the 2009 and 2016 year-lines having more than 50% higher biomass than the nontreated control.

CONCLUSION

This study demonstrates that weeds can rapidly evolve increased competitive ability. Furthermore, the results indicate the possibility of changes in glyphosate hormesis over time. These results highlight the importance of the role that rapid (i.e., subdecadal) evolution of growth traits might have on the sustainability of weed management strategies. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Low-dose chemical stimulation and pest resistance threaten global crop production

Pesticide resistance increases and threatens crop production sustainability. Chemical contamination contributes to the development of pest resistance to pesticides, in part by causing stimulatory effects on pests at low sub-toxic doses and facilitating the spread of resistance genes. This article discusses hormesis and low-dose biological stimulation and their relevance to crop pest resistance. It highlights that a holistic approach is needed to tackle pest resistance to pesticides and reduce imbalance in accessing food and improving food security in accordance with the UN's Sustainable Development Goals. Among others, the effects of sub-toxic doses of pesticides should be considered when assessing the impact of synthetic and natural pesticides, while the promotion of alternative agronomical practices is needed to decrease the use of agrochemicals. Potential alternative solutions include camo-cropping, exogenous application of phytochemicals that are pest-suppressing or -repelling and/or attractive to carnivorous arthropods and other pest natural enemies, and nano-technological innovations. Moreover, to facilitate tackling of pesticide resistance in poorer countries, less technology-demanding and low-cost practices are needed. These include mixed cropping systems, diversification of cultures, use of 'push-pull cropping', incorporation of flower strips into cultivations, modification of microenvironment, and application of beneficial microorganisms and insects. However, there are still numerous open questions, and more research is needed to address the ecological and environmental effects of many of these potential solutions, with special reference to trophic webs.

Hormesis induced by silver iodide, hydrocarbons, microplastics, pesticides, and pharmaceuticals: Implications for agroforestry ecosystems health

Increasing amounts of silver iodide (AgI) in the environment are expected because of the recent massive expansion of weather modification programs. Concurrently, pharmaceuticals, microplastics, hydrocarbons, and pesticides in terrestrial ecosystems continue contaminating forests and agroforests. Our review supports that AgI induces hormesis, a biphasic dose response characterized by often beneficial low-dose responses and toxic high-dose effects, which adds to the evidence for pharmaceuticals, microplastics, hydrocarbons, and pesticides induced hormesis in numerous species. Doses smaller than the no-observed-adverse-effect-level (NOAEL) positively affect defense physiology, growth, biomass, yields, survival, lifespan, and reproduction. They also lead to negative or undesirable outcomes, including stimulation of pathogenic microbes, pest insects, and weeds with enhanced resistance to drugs and potential negative multi- or trans-generational effects. Such sub-NOAEL effects perplex terrestrial ecosystems managements and may compromise combating outbreaks of disease vectors that can threaten not only forest and agroforestry health but also sensitive human subpopulations living in remote forested areas.

Effect of low glyphosate doses on flowering and seed germination of glyphosate-resistant and -susceptible Digitaria insularis

BACKGROUND

Herbicide hormesis is characterized by stimulation of various growth and developmental parameters, such as biomass and height, at low herbicide doses. Other possible hormetic effects are earlier flowering, higher seed weight, more seeds, and a shorter plant life cycle, which could favor the propagation of the species. This study tested the early flowering in glyphosate-resistant and -susceptible Digitaria insularis biotypes under treatment with low glyphosate doses.

RESULTS

Hormesis caused by low glyphosate doses occurred in all experiments. The hormetic effects were a decrease in time necessary for the formation of inflorescences and increased seed weight and germination speed. Higher glyphosate doses were required for the hormetic effect in the glyphosate-resistant than the -susceptible D. insularis biotype.

CONCLUSIONS

Hormesis caused by low glyphosate doses in D. insularis may provide an advantage for the dissemination of this species, helping to alter the weed flora. As the doses that cause stimulation in glyphosate-resistant biotypes are higher than in glyphosate-susceptible biotypes, the selection of resistant biotypes may be favored in glyphosate-sprayed fields, increasing the rate of infestation of glyphosate-resistant biotypes.

A gift from parent to offspring: transgenerational hormesis

Hormesis is a biological phenomenon characterized by opposite effects between low and high doses of stresses that can result in stimulatory and adaptive benefits to individuals within a population. While evidence of hormesis is well established, two recent studies (Nogueira et al., Belz and Sinkkonen) suggest that hormesis can also offer transgenerational benefit.